Conventionally, power supply apparatuses such as switching power sources or power supply circuits that supply electrical power (voltage or current) from a power source to a load circuit have been used in electronic circuits or electronic equipments. Such power supply apparatus may be implemented, for example, as DC-DC converter devices.
Electronic equipments in recent years have been desired to have lower power consumption and standby power requirement. Load circuit operations include some modes that require high power and other modes that require low power. In particular, most electronic equipments include a central processing unit (hereinafter referred to as “CPU”) and software that is run on the CPU. CPU operations often include some modes that require high power and other modes that require low power, and software, too, often includes some modes that require high power and other modes that require low power. For example, when the software is performing only a display function, the CPU on which the software is running requires low power, while, when the software is performing calculations, the CPU on which the software is running requires high power.
Conventional power supply apparatuses include a power source, a pulse switch that controls the level of power sent from the power source in accordance with pulse width (pulse width modulation or PWM), and a driver that controls the opening and closing of the pulse switch. A power supply apparatus with such a configuration could vary the level of power supplied to the load circuit only to a limited extent and could not sufficiently reduce power consumption in the low power mode or standby mode.
In a power supply apparatus with such a configuration, there were limitations in varying a level of power supplied to the load circuit, and it was impossible to sufficiently reduce power consumption in the low power mode or standby mode.
Another problem particularly associated with switching power sources is that, since the main circuit unit that transmits electrical power to a load is designed to have device characteristics suited for heavy load applications that require a large load current, it is difficult to improve power efficiency of the main circuit unit for light load applications that require only a small load current.
Accordingly, a hybrid type power supply apparatus (DC-DC converter) has been proposed (see, for example, Patent Document 1), which includes a plurality of paths for respectively supplying different levels of power to a load circuit, and a driver that switches between the plurality of paths.    Patent Document 1: Japanese Published Unexamined Patent Application No. 2007-221981